With respect to light-emitting element modules which mount and package light-emitting elements such as LEDs, a surface-mount type package structure like that shown in FIG. 10 has heretofore been used when attempting to miniaturize the packaging structure. In this light-emitting element module, a concave portion is provided in a substrate 3 composed of resin or ceramic, two positive/negative electrodes 4, 4 are arranged on the bottom face of the concave portion, and a light-emitting element 1 is electrically connected and fixed to one of the electrodes 4 via conductive paste or the like. The top side of the light-emitting element 1 is electrically connected to the other electrode 4 by a wire bonding 2 such as gold wire. These electrodes 4, 4 extend to the exterior of the substrate. After mounting the light-emitting element 1, the concave portion is filled with a sealing resin 5 of high optical transmittance such as epoxy resin, and the sealing resin 5 is cured to seal the light-emitting element 1. Particularly in the case of white LEDs, a blue LED is used as the light-emitting element, and a blue-excited yellow-emitting fluorescent material is mixed into sealing resin which is similarly used to fill the reflective concave portion.
Heretofore, as applications which mount numerous light-emitting elements on one substrate, dot matrix units which are lighting devices and display devices have been common. To enable mounting of numerous light-emitting elements such as LEDs, these devices generally mount numerous light-emitting elements on a substrate made of glass-fiber-reinforced epoxy resin or the like, and are commercialized as unit products, A substrate for this type of LED unit is disclosed, for example, in Patent Document 1.
As a conventional structure of this LED unit, one may adopt a structure in which numerous bullet type LEDs are mounted onto an electronic substrate, or a form in which numerous surface-mount type LEDs are mounted. To manufacture this unit it is necessary to adopt a process wherein the bullet type or surface-amount type LEDs are fabricated, and electrically connected by soldering or the like to an electronic substrate on which an electronic circuit pattern that suits their needs has been prepared. Accordingly, it is necessary to have a two-stage production process pertaining to the bullet type or surface-mount type LEDs and the LED units in which they are assembled.
With respect to the manufacture of light-emitting element modules such as LED units, a manufacturing method referred to as the chip-on-board method, in which light-emitting elements are directly mounted onto an electronic substrate, is becoming major in recent years. By directly mounting the light-emitting elements onto an electronic substrate, this method has the advantage of obviating the aforementioned process of semi-finished productions, and also enabling simplification of structure.
On the other hand, when mounting light-emitting elements such as LEDs onto a substrate, it is necessary to adopt a packaging structure having reflective cups which are concave portions with sloped reflective surfaces in order to orient the direction of optical emission in the forward direction. The form of this reflective cup has the functions of controlling light-emitting conditions by appropriately designing and holding the resin that seals the light-emitting element. Furthermore, in conjunction with the increasingly high light-emission intensities of light-emitting elements in recent years, it has become important to endow the electronic substrate on which the light-emitting elements are mounted with a heat dissipation function.
In light of these demands, as shown in FIG. 11, a structure has come to predominate in which a substrate is provided with a heat dissipation metal board 8 such as aluminum board or copper board and an insulating layer 7 provided on the board 8. The LED unit shown in FIG. 11 adopts a structure wherein the insulating layer 7 is provided on the heat dissipation metal board 8, multiple electrodes 4 are provided on the insulating layer 7, light-emitting elements 1 are provided on these electrodes 4, the top side of the respective light-emitting element 1 is electrically connected to the adjacent electrode by a wire bonding 2, a reflective board 6 which has multiple holes having sloped parts 6a is placed so that the respective light-emitting element 1 is positioned at the center of the hole, and the light-emitting elements 1 are scaled by filling the respective holes with sealing resin 5 and then curing the sealing resin 5. FIG. 12 is a plan view of the state where the light-emitting elements 1 are mounted on the substrate. This structure is disclosed, for example, in Patent Document 2.
The electrode structure of this case is shown in FIG. 13, and its electrical circuit configuration is shown in FIG. 14.
A light-emitting element module of the chip-on-board method is generally manufactured by the following process.
1. A light-emitting element is mounted on an electrode in a reflective cup of a substrate by using silver paste or, when the electrode material of the light-emitting element is AuSn or the like, by a so-called eutectic soldering—a connection in which heat and vibration are imparted—resulting in electrical continuity. Furthermore, the light-emitting element is connected to a counter electrode by a wire bonding. With respect to light-emitting elements having electrodes on only one side, two positive/negative electrodes are both subjected to wire bonding. Furthermore, with respect to light-emitting elements having electrodes on only one side, it is also possible to connect by flip-chip packaging via bumps composed of gold or the like arranged on top of the electrodes.
2. The interior of the reflective cup is filled with sealing resin, curing treatment is performed by a method of curing the employed resin such as heat curing or UV curing, and molding is conducted. In cases where the fabricated light-emitting element module is a white LED module, a fluorescent material is intermixed with the sealing resin in advance before curing.
3. A lens body made of resin, glass or the like may be combined as necessary with the top of the sealing resin and the top of the light-emitting element module.
On the other hand, when undertaking to directly mount light-emitting elements onto the substrate without providing reflective cups, as shown in FIG. 15, one may also conceive of a method where electrodes 12 are disposed on a flat substrate 11, light emitting elements 9 and wire bondings 10 are mounted onto the electrodes 12 by the same method described above, and sealing resin 13 is molded by a molding method such as transfer molding such that the light-emitting elements 9 and wire bondings 10 are subjected to resin sealing. However, with this method, it is difficult to dispose the sealing resin 13 in accurate positions due to problems such as the dimensional tolerance of the substrate. Furthermore, in the case of white LEDs, as fluorescent material is intermixed with the sealing resin 13, when the form of the sealing resin 13 is unstable, variations arise in the distance pertaining to the passage of the light emitted from the light-emitting elements 9 through the interior of the sealing resin 13 containing fluorescent material, thereby becoming difficult to control the color as required.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2001-332768.
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2001-332769.